A little discussed feature of other planets is holidays. I'm not talking about Chrismanukwanza or Conjoined President's Day or similar holidays brought from Earth. I'm talking about local celebrations to baffle and thrill your players.
There's a lot of fiction written about festivals where everyone is entitled to do whatever they wish with no repercussions. Star Trek: TOS started that trope and it's gotten dumber with every iteration. If you think you could rape and murder without abandon and your victims and their relatives would just let it slide after some arbitrary alarm goes off you're an idiot. Just let one member of the 1% be grabbed by blue collar celebrants and believe me there will be consequences. I want to talk about happier times to be had by all (npcs and pcs, no really).
The first problem with Earth style holidays is when to celebrate them. Other planets are unlikely to have a year and day the same length as Earth. Tidally locked worlds are even worse. One day equals one year. How do you divide that up? Either the locals will pick a local day roughly equivalent in their calendar or celebrate whenever that day hits on Earth, which means Christmas, for example, will move around on local calendars or even come up twice in one year.
I suppose you could figure out the equivalent day locally by establishing the different seasons using Vernal and Autumnal Equinoxes and the Summer and Winter Solstices and figuring each date by the percentage of the season it occurs in. On a planet with a long year you're going to get hosed for birthday presents though. On tidally locked planets and vacuum worlds the locals might just go with the terran calendar system and screw how high the sun is in the sky.
Planets with exceptionally long years might have a few made up holidays to fill in the gaps. Holidays could celebrate local events. First Landing Day could be celebrated by giving out presents to fill the void in a 486 day year. On the other hand First Landing Day could be a somber occasion mourning those who lost their lives merely reaching their new home. Or there could be different ways different groups celebrate the same day. Store owners try to turn 1stLD into a carnival like celebration to make credits while many conservative elders frown on this and prefer quiet services held at home. Know your audience is the rule here.
Holidays marked by a phase of Luna might be thrown way off. No moon is bad enough but what about when you have three moons and no one agrees which one to follow? Hilarity ensues.
Holidays can be marked by sports, special foods, dance, costumes, and nearly anything else you could think of. On Peraspera a young person's rite of adulthood is held on the Vernal Equinox. they must remove their breathing gear and descend into the poisonous low lands, holding their breath for 30 seconds. In the Scout Service Memorial Day recognizes the fallen Scouts and their heroism by having the youngest member of each ship's crew attempt reentry on a suitable world using a vacc suit (+7 survival rolls, remember?)
Some planets may celebrate the Earth they left behind. Thanksgiving or an autumnal feast celebrating the harvest is pretty universal (except on space colonies, they grow crops year round). Of course the colonists on Nergal find it expensive to import turkeys from Terra and instead eat the native land decapod. But hey, everyone gets a drumstick! Holidays may change with time, isolation and as the colonists create their own cultures.